[Ifeffit] Interpreting old XANES data with missing standards

[Don Baker]

Hi Matthew,

Thanks for your ideas and even more for the spectra.  I looked at the
ESRF data base before, but forgot to mention it in my original email.
We tried our best to avoid radiation damage and found little-to-no
evidence of it in our samples when we compared our standards (a series
of iron sulfides and alkali sulfites and sulfates) by comparison with
previously measured spectra.

The dominant sulfur species in our glasses is sulfide based upon both
XANES and electron microprobe peak shift measurements.

Wishing you a great weekend,

Don



On Fri, 2018-06-08 at 09:01 -0700, Matthew Marcus wrote:
> Dear Don.  Regarding yours of Fri, 08 Jun 2018 09:54:40 -0400:
> 
> ESRF has a dbase of S XANES, but they're all pretty affected by overabsorption ("self-absorption").  I think the only reliable way to take such data is in TEY mode.
> There's a spectrum there for cinnabar (remember, there are multiple polymorphs of HgS) and three forms of Fe sulfide plus several more sulfides.  Even the transmission spectra are subject to
> hole effect, which looks like overabsorption.
> Also, if you do take data on sulfides, beware of radiation damage.
> 
> Does it really make sense that a silicate glass would have sulfide in it?  I'd think that it would have mostly sulfate and maybe sulfite.  Check the peak position;
> it's a pretty reliable indicator of sulfite vs. sulfate vs. other.
> 
> Here are some spectra taken in TEY mode with the calibration gypsum = 2482.75eV.
> 
> Sincerely,
>     Matthew Marcus
> > Hello All,
> > 
> > First let me apologize if the question below is inappropriate for this
> > group, but I don't know of a better set of experts that I can ask.
> > 
> > So, here is some background:
> > 
> > I have some old S K-edge XANES data from NSLS X15B for S-bearing
> > silicate glasses that was collected by a Ph.D. student who decided to
> > leave for a good job rather than finishing their degree.  During my
> > current sabbatical year I have been looking at the data and reading
> > papers on the topic.  I think that I now understand, at least
> > qualitatively, the changes in the spectra as a function of iron
> > concentration in the glasses, but to perform quantitative modelling I
> > need XANES spectra of MgS and CaS, which we did not think to collect all
> > those years ago.  I have searched for XANES spectra of MgS and CaS on
> > the CARS XAFS Data Library and on the XAFS Database at IIT without
> > success.  I am unaware of other databases available.
> > 
> > Now for for my questions:
> > 
> > 1.  Does anyone know of a XANES database that contains MgS and CaS
> > spectra?  (Or did I miss it in the databases I searched?)
> > 
> > 2.  If I cannot find measured MgS and CaS spectra, what do you think
> > about using calculated spectra (e.g., Zheng et al.,2012, NPJ
> > Computational Materials, 12 -- which uses FEFF) for quantitative
> > modelling?
> > 
> > 
> > And information, ideas, and suggestions that you may have will be
> > appreciated.
> > 
> > 
> > Wishing you all the best from a spring morning in Montreal,
> > 
> > Don
> > 
> >   
> > 
> > 
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-- 
Melting rocks today for a better tomorrow . . . 
Don R. Baker, Professor of Geochemistry, Earth and Planetary Sciences,
McGill University